1. Field of the Invention
The present invention relates to a projection type display device, and more particularly to a projection type display device capable of achieving color separation and color combination simultaneously by using a pair of dichroic mirrors, and thus making the overall arrangement simple.
2. Description of the Prior Art
Referring to FIG. 1, there is illustrated a conventional projection type display device using reflection type displays. As shown in FIG. 1, the display device comprises a dichroic prism 1, three lamps 2a, 2b and 2c disposed at three places around the dichroic prism 1, respectively, red (R), green (G) and blue (B) color filters 3a, 3b and 3c disposed downstream of respective lamps 2a, 2b and 2c, condensing lenses 4a, 4b and 4c disposed downstream of respective color filters 3a, 3b and 3c, and total reflection mirrors 5a, 5b and 5c disposed downstream of respective condensing lenses 4a, 4b and 4c. Each of the total reflection mirrors 5a, 5b and 5c has a central aperture.
The display device also comprises field lenses 6a, 6b and 6c disposed oppositely to the dichroic prism 1 with respect to respective total reflection mirrors 5a, 5b and 5c and image displays 7.sub.R, 7.sub.G and 7.sub.B associated with respective field lenses 6a, 6b and 6c. A projection lens 8 is also disposed downstream of the dichroic prism 1.
In accordance with the above-mentioned arrangement of conventional projection type display device, respective lights emitted from the lamps 2a, 2b and 2c are transmitted to the color filters 3a, 3b and 3c disposed downstream of the lamps 2a, 2b and 2c. The color filters 3a, 3b and 3c serve to allow different monochromatic components, namely, R, G and B color beams of the lights to pass therethrough, respectively. These R, G and B color beams are focused by the condensing lenses 4a, 4b and 4c onto the pointing total reflection mirrors 5a, 5b and 5c and then reflected from the total reflection mirrors 5a, 5b and 5c respectively. The R, G and B color beams are transmitted through respective field lenses 6a, 6b and 6c and thus changed into parallel beams. These parallel beams illuminate the image displays 7.sub.R, 7.sub.G and 7.sub.B. These R, G and B color beams illuminating the image displays 7.sub.R, 7.sub.G and 7.sub.B are then reflected to be transmitted through the field lenses 6a, 6b and 6c respectively. The field lenses 6a, 6b and 6c serve to reverse the paths of R, G and B color beams so that the R, G and B color beams are focused at respective central apertures of total reflection mirrors 5a, 5b and 5c and then transmitted through the same central apertures to the dichroic prism 1.
In the dichroic prism 1, the R, G and B color beams incident in three directions travel their predetermined reflection and transmission paths and then a combination path. At the combination path, the R, G and B color beams are combined into a full color beam which is, in turn, transmitted to the projection lens 8 disposed downstream of the dichroic prism 1. The full color beam combined in the dichroic prism 1 is enlarged by the projection lens 8 and then projected onto a screen 9 disposed downstream of the projection lens 8 to produce an image on the screen 9. Thus, the full color image is displayed on the screen 9.
However, the above-mentioned projection type display device equipped with conventional reflection type image display has a complex arrangement requiring many constituting elements, since it uses three sets of lamps, color filters, condensing lenses and total reflection mirrors, for achieving a R, G and B color or separation. The conventional display device also has a disadvantage of an expensive manufacture cost, in that it uses the dichroic prism which is expensive and difficult to be manufacture.
Furthermore, the conventional display device has a disadvantage of an inefficiency in light utilization, since a color filter functions to transmit only one among R, G and B beams of each of the lights emitted from three lamps and absorb the remainders, thereby causing the utilization rate of light emitted from each lamp to be reduced by 1/3.